1. Field of the Invention
The present invention relates to a high-frequency Colpitts circuit, and especially relates to the high-frequency Colpitts circuit, which realizes a stable circuit while ensuring a negative resistance at a high frequency.
2. Description of the Related Art
[Conventional Colpitts Circuit: FIG. 6]
A conventional Colpitts circuit is described with reference to FIG. 6. FIG. 6 is a configuration diagram of the conventional Colpitts circuit.
As shown in FIG. 6, the conventional Colpitts circuit is provided with a terminal (Port P1) to which a crystal oscillator is connected and a transistor Q1 for amplifying an oscillation frequency of the crystal oscillator in which the terminal is connected to a base of the transistor Q1, a supply voltage (V_DC) is applied to a collector of the transistor Q1 through a resistance R3, further the supply voltage is connected to the base through a resistance R1 and the base is grounded through a resistance R2.
Also, an emitter of the transistor Q1 is grounded through a resistance R4 and the base is grounded through capacitors C1 and C2 connected in series, and a point between the capacitors C1 and C2 is connected to the emitter. Then, an output terminal for outputting an amplified oscillation frequency from the collector is provided.
Also, a negative resistance characteristic in the Colpitts circuit in FIG. 6 is shown in FIG. 7. FIG. 7 is a view showing the negative resistance characteristic of the conventional Colpitts circuit. In FIG. 7, an abscissa axis represents a value of the frequency and a longitudinal axis represents a value of the negative resistance.
In FIG. 7, the negative resistance is realized at 200 MHz or higher.
Meanwhile, as the related conventional art, there is Japanese Patent Application Laid-Open (JP-A) No. 2007-116487 “High-Frequency Colpitts Oscillation Circuit” (Applicant: Epson Toyocom Corporation).
JP-A No. 2007-116487 discloses the high-frequency Colpitts circuit provided with the Colpitts oscillation circuit and the collector-grounded amplification circuit in which the output terminal of the Colpitts oscillation circuit is connected to the input terminal of the collector-grounded amplification circuit, and the output of the collector-grounded amplification circuit is fed back to the Colpitts oscillation circuit.
Also, as another conventional art, there is JP-A No. 2004-266583 “Piezoelectric Oscillator” (Applicant: TOYO Communication Equipment Co., Ltd.).
JP-A No. 2004-266583 discloses the configuration of the Colpitts-type piezoelectric oscillator in which the signal from the emitter of the transistor is fed back to the base, and further the resonance circuit for controlling the negative resistance is provided on the emitter side.
Also, as another conventional art, there is JP-A No. 2004-304667 “Piezoelectric Oscillator” (Applicant: TOYO Communication Equipment Co., Ltd.).
JP-A No. 2004-304667 discloses the configuration of the Colpitts-type piezoelectric oscillator in which the signal from the source of the FET transistor TR2 is fed back to the base of the oscillation transistor TR1, and the parallel synchronization circuit for controlling the oscillation frequency is provided on the drain side of the FET transistor.